1. Field of the Invention
The present invention relates to the treatment of fractures of the odontoid apophysis of the axis, or second cervical vertebra C2, and in particular, to means of containment after reduction of the osseous fragments to be fused.
Specifically, the invention relates to a plate of a shape intended to be fixed onto the third cervical vertebra C3, serving to support a screw threaded into the axis C2 to assure interfragmentary compression there in order to provide solidarity for the osseous fragments.
The odontoid apophysis or dens of the axis C2 is the essential mechanical organ for articulation of the atlas, or first cervical vertebra C1, which supports the occipital bone. It is particularly around this vertebra that all the movements of head rotation are produced. Because of this functional requirement and its corresponding shape, the odontoid apophysis is a zone of convergence of accidental forces which affect the cervical column and is therefore a zone particularly subject to fracture, with the fracture assuming a perfectly characteristic form. These fractures have been difficult to treat in a sufficiently reliable manner.
2. Discussion of the Prior Art
In the case of stable fractures, the osseous fragments can be immobilized by bringing the fragments together using a conventional external apparatus such as a compression brace. This brace however can only be used for stable fractures, where the separated fragments do not have the tendency of separating after reduction, or where there is neither anterior nor posterior displacement of the atlas C1.
In the case of unstable fractures, it is therefore necessary to use surgical techniques. These are relatively numerous, but all those currently known have major inherent insufficiencies or disadvantages. The techniques can be classified into three groups:
In mixed extra-articular arthrodesis by the posterior cervical route, the atlas C1 and the axis C2 are brought together with a metal band or a non-resorbable suture by their posterior cervical arcs. A graft is added in situ, in order to assure joining by the biological fusion of the two vertebral posterior arcs in case of rupture of the osteosynthesis suture. Under these conditions, if consolidation of the fractured odontoid apophysis does not occur, a graft is placed on the posterior arcs of C1 and C2. This combination of a band and a graft is very reliable, but the bonding of the arcs noticeably constrains head rotation. In addition, it is not practicable to allow this disabling technique to exist. While a simple band without a graft eliminates this defect, it remains too hazardous to maintain due to the possibility that the band suture may rupture.
In direct osteosynthesis by the transbuccal route, the surgeon, passing through the buccal cavity, makes an incision in the pharynx behind the base of the tongue. He then intervenes directly on the fractured odontoid apophysis onto which a consolidation plate is screwed. This technique is relatively simple and logical, but passing through the oropharynx can create serious septic complications.
In osteosynthesis by the anterior presterno-mastoid route, the odontoid apophysis is accessed first by the cervical route at the level of the anterior face of the neck, passing in front of the sterno-cleido-mastoid muscle. This technique, recommended by J. BOEHLER, carries out interfragmentary compression of the dens (odontoid apophysis) with screws, and is performed under radioscopic display with a brightness amplification. One or more screws are used, which can perforate the cranial extremity (located at the side of the cranium) of the dens. This method of operation is frequently used by doctors because it does not have the disadvantages of the other two methods discussed above. It is, however, encumbered with mechanical imperfections in its current state of development, which hinder its usefulness.